It is often necessary to remove heat from heat sources. One example of a heat source is an electronic device. Electronic devices, such as integrated circuit devices, are increasingly being used in modern applications. One prevalent example is the computer. The central processing unit or units of most computers, including personal computers, is constructed from an integrated circuit device.
During normal operation, electronic devices generate significant amounts of heat. If this heat is not continuously removed, the electronic device may overheat, resulting in damage to the device and/or a reduction in operating performance. In order to avoid such overheating, various types of cooling devices have been developed for use in conjunction with electronic devices.
One type of cooling device is a heat sink cooling device. In such a device, a heat sink is formed of a material, such as aluminum, which readily conducts heat. The heat sink is usually placed on top of and in contact with the electronic device. Due to this contact, heat generated by the electronic device is conducted into the heat sink and away from the electronic device.
The heat sink may include a plurality of cooling fins in order to increase the surface area of the heat sink and, thus, maximize the transfer of heat from the heat sink into the surrounding air. In this manner, the heat sink draws heat away from the electronic device and transfers the heat into the surrounding air. An example of a heat sink is disclosed in U.S. Pat. No. 5,794,685 of Dean for HEAT SINK DEVICE HAVING RADIAL HEAT AND AIRFLOW PATHS, which is hereby incorporated by reference for all that is disclosed therein.
In order to enhance the cooling capacity of a heat sink device, an electrically powered fan is often mounted within or adjacent to the heat sink. In operation, the fan causes air to move over and around the fins of the heat sink device, thus cooling the fins by enhancing the transfer of heat from the fins into the ambient air. Examples of heat sink devices including fans are disclosed in U.S. Pat. No. 5,785,116 of Wagner for FAN ASSISTED HEAT SINK DEVICE and U.S. Pat. No. 5,740,013 of Roesner et al. for ELECTRONIC DEVICE ENCLOSURE HAVING ELECTROMAGNETIC ENERGY CONTAINMENT AND HEAT REMOVAL CHARACTERISTICS, which are both hereby incorporated by reference for all that is disclosed therein.
Over the years, as the power of electronic devices has increased, so has the amount of heat generated by these devices. In order to adequately cool these higher powered electronic devices, cooling devices with greater cooling capacities are required. One strategy for increasing cooling capacity is to provide a heat sink having a base portion with a surface area larger than the surface area of the electronic device being cooled. As can be appreciated, this large area base portion provides a larger radiating surface for dissipating heat into the surrounding air, and thus enhances heat removal from the heat sink. If cooling fins are used, as described above, the larger base portion also allows a greater number of cooling fins to be attached to the heat sink than would otherwise be possible.
One problem with the larger base portion heat sink described above, is that heat from the electronic device must first travel or conduct through the material forming the base portion before reaching the larger radiating surface. Although materials exhibiting relatively high thermal conductivity, e.g., aluminum and copper, are commonly used in the construction of heat sink devices, even these materials result in an undesirable level of thermal resistance which decreases the cooling ability of the heat sink device.
In order to address this problem, it is known to provide a heat pipe in association with a heat sink device. The heat pipe is generally located between the heat source being cooled and the larger radiating surface described above. Such a heat pipe generally comprises a partially evacuated chamber which includes a small quantity of working fluid, e.g., water. One wall (the heating wall) of the heat pipe is placed in contact with the heat source while another wall (the radiating or condensing wall) of the heat pipe is located adjacent the radiating surface of the heat sink. In the operation of such a device, the heat source raises the temperature of the heat pipe heating wall, causing the working fluid to vaporize. The resulting vapor then spreads rapidly throughout the heat pipe chamber, ultimately condensing on the cooler radiating wall. Thus, within the heat pipe, heat from the heating wall is transferred to the radiating wall via the latent heat of vaporization of the working fluid. Generally, the use of a heat pipe arrangement, as described above, allows heat to transfer from one surface to another more efficiently than if the heat were merely conducted through a solid material such as aluminum or copper. Examples of cooling devices incorporating heat pipe technology are described in U.S. Pat. No. 5,694,295 of Mochizuki et al. for HEAT PIPE AND PROCESS FOR MANUFACTURING THE SAME, which is hereby incorporated by reference for all that is disclosed therein.
Although the cooling devices described above generally work well in many applications, it is always desirable to further improve the efficiency and heat removal ability of cooling devices, particularly in view of the increasing cooling needs outlined above.